In Smart Power integrated circuits (ICs), the current through a load transistor is measured using a sense transistor. The current in the load MOSFET is measured using a second MOSFET that has much smaller area. Ideally, the sense transistor and the load transistor are operated at the same operating point in which the transistors' source, gate, and drain voltages are identical. The ratio of the currents in the load and sense transistors is called KILIS (“K”):
                    K        =                              I            ⁡                          (              load              )                                            I            ⁡                          (              sense              )                                                          (                  Eq          .                                          ⁢          1                )            
The accuracy of K is an important characteristic of Smart Power ICs. However, scattering causes K to vary in each production due to several factors. At low drain currents, the two most important factors are the threshold voltage mismatch between the transistors and the voltage difference between the load and sense source voltages (source voltage offset).
The problem of minimizing the scatter of K at low currents is not solved by known techniques. Currently, two operation modes are typically used—normal operation and gate-back regulation. In normal operation, the load and sense transistors are operated at a constant gate voltage. In the low current regime, the drain voltage is very small and the source voltage offset leads to linear increase of the scatter in K with decreasing drain current. In gate-back regulation, the transistors are operated at constant drain voltage. In the low current regime, the gate overdrive (the gate-threshold voltage difference ) is very small and the threshold voltage mismatch between the transistors leads to a linear increase of the scatter in K with decreasing drain current.